The invention relates to an electronic commutation method in direct current electric motors.
In electronically commutated direct current electric motors, the rotating magnetic field necessary for the rotational movement is controlled by suitable electronics. The exact instants of commutation depend on the rotor position of the motor, which is either detected by means of sensors or by measuring the counter-induction voltage (back EMF) of the phase which is not energized at the time. Sensorless commutation detection can be carried out by using comparators for detecting the zero crossovers of the induced voltage and evaluating the comparator signals. It is also known to measure the induced voltage directly and to compare the measured values with a threshold about the zero crossover.
A method for measuring the current consumption of an electric motor which is supplied from a direct voltage network and controlled by pulse width modulation (PWM) is disclosed in DE 10 2005 006 503 A1. A PWM control unit supplies pulse width modulated voltage control signals for a semiconductor switching device, by means of which the current flow in the electric motor is controlled. The voltage drop, from which the motor current is inferred is measured at a measuring resistor connected in series with the semiconductor switching device.